Button click event not getting not fired which is placed inside a panel for Model popup extender.

Hi ,
i am new to web application development and i have a problem in my code with button click event. i am using a model popup extender control so inside the panel i have a button. on click of which i need to write some code in the code behind but all that is stopping me to do so is Button Click Event for that button. which is not getting fired. and model popup is fine.
here is my code follows.
<asp:Panel ID="pnlpopup" runat="server" BackColor="White" Height="269px" Width="400px" >
<table width="100%" style="border: Solid 3px #D55500; width: 100%; height: 100%"
cellpadding="0" cellspacing="0">
<tr style="background-color: Silver">
<td colspan="2" style="height: 10%; color: Black; font-weight: bold; font-size: larger"
align="center">
Manufacture Details
</td>
</tr>
<tr style="background-color: Silver">
<td class="style28">
Manufacture Name :
</td>
<td >
<asp:Label ID="lblusername" runat="server"></asp:Label>
</td>
</tr>
<tr style="background-color: Silver">
<td colspan="2" >Please Select the Manufacture if already existed <br /> in the Database</td>
</tr>

<tr style="background-color: Silver">
<td colspan="2" valign="top" class="style27">
<asp:Panel ID="pnlManufacture" runat="server" ScrollBars="Auto" Height="116px"
Width="394px">
<table><tr><td align ="center"><asp:RadioButtonList ID="rdblManufacture"
runat="server" Height="113px" Width="377px"></asp:RadioButtonList></td></tr></table>
</asp:Panel>
</td>
</tr>
<tr style="background-color: Silver">
<td align="center" colspan="2">
<asp:Button ID="btnUpdate" runat="server" CommandName="Update"
Text="Update" OnClick="btnUpdate_Click" /> &nbsp;&nbsp;
<asp:Button ID="btnCancel" runat="server" Text="Cancel" />
</td>
</tr>

</table>
<span style="display: none">
<asp:Button ID="btnInvisCancel" runat="server" />
</span>
</asp:Panel>



code behind :

protected void btnUpdate_Click(object sender, EventArgs e)
{

}

sateesh kumar singupuram